Ping Pong Math node - what does it do?
It's a positive symmetrical triangle-wave, amplitude Scale, period  2 * Scale, 0 at 0.

Here's the function illustrated with 'Scale' (from the bottom up) set to 1, 0.5, and 0.333.
These planes are 8 units across, and 2 up, 0 at center.
You could roll your own like this:
PingPong(Value) = Scale - abs( (abs(Value) % (2*Scale)) - Scale)

..but someone else might come up with a neater way.. :)
You could wrap up the node like this to give more intuitive inputs?